In Achlya, a filamentous aquatic mold, the formation and conjugation of the sex organs are initiated and regulated by steroids called hormones A and B. Hormone A, named antheridiol, has been isolated, characterized and synthesized at The New York Botanical Garden. We are attempting now to isolate and characterize hormone B, which initiates the formation of oogonial branches. Hormone B is extracted with methylene chloride from the culture fluid of the hermaphroditic strain 8-6 of A. heterosexualis grown in aerated carboys. Hormone B extracted is purified first by column chromatography and then the active, crystalline solids are separated by TLC into a slower moving, inactive band and a faster-moving, active band.